1. FIELD OF THE INVENTION
This invention relates to a device for rotatably driving a small-sized disk, such as a 3.5-inch floppy disk by supporting the disk and, more particularly, to a disk rotatably driving device in which a load caused by engaging a driving pin when chucking the hub at the center of the disk is reduced.
2. DESCRIPTION OF THE PRIOR ART
FIGS. 7 to 9 show a floppy disk rotatably driving device provided in a conventional 3.5-inch floppy disk driving unit.
In FIGS. 7 to 9, reference numeral 1 designates a rotatably driving shaft. The driving shaft 1 is rotatably driven by a brushless DC motor. A circular turntable 2 is fixed to the upper end of the driving shaft 1, and the upper end 1a of the driving shaft 1 is projected upward from the center of the turntable 2. The turntable 2 is composed of a disk 2a made of a ferromagnetic material, and an element base 2b having a peripheral pole section M formed on the disk 2a. A slider plate 4 made of synthetic resin is fixed to the center on the upper surface of the turntable 2. A through hole A is formed at the turntable 2, and a driving pin 5 fixed to the end 3a of a leaf spring 3 fixed to the lower surface of the turntable 2 is projected via the through hole A from the upper surface of the turntable 2.
Reference numeral 6 in FIG. 7 designates a hub fixed to the center of a disk 7 inserted to between the upper side 8a and the lower side 8b of a disk cartridge 8. In case of 3.5-inch floppy disk, the hub 6 is made of a thin metal plate, and, as shown in FIG. 9, a central hole 6a of substantially square shape is perforated at the center, and a driving hole 6b of substantially rectangular shape is perforated at a position separated at a predetermined distance from the centeral hole 6a.
As shown in FIG. 9, when the hub 6 is mounted on the rotating turntable 2, the driving pin 5 is, for example, slid on the lower surface of the hub 6 at a position (a), the end 3a of the leaf spring 3 is deflected downward at this time, and the driving pin 5 is moved backward from the upper surface of the turntable 2. When the turntable 2 is rotated so that the driving pin 5 is inserted into the driving hole 6b of the hub 6 to arrive, for example, at a position (b), the driving pin 5 is projected from the upper surface of the turntable 2 and inserted into the driving hole 6b of the hub 6 by the elastic force of the end 3a of the leaf spring 6. When the turntable 2 is further rotated, the driving pin 5 is first contacted with the outer side 6c of the driving hole 6b of the hub 6, and then contacted with the front side 6d while contacting with the outer side 6c of the driving hole 6b during the slight inclination toward the center. The hub 6 is positioned radially in the rotating direction with respect to the turntable to be rotatably driven at a position (c).
However, in such a conventional disk rotatably driving device, a force for magnetically attracting the hub 6 of the disk is weakened at the periphery of the driving pin 5 to collapse the magnetic balance since the pole section M of the element base 2b of the turntable 2 is formed over the entire periphery as shown in FIG. 8. For example, when the hub 6 of the disk is chucked at the position (a) in FIG. 9, the magnetically attracting force is weak at the periphery of the through hole A of the element base 2b as shown in FIG. 10 and the opposite side of the hub 6 might be accordingly contacted fixedly with the pole section M of the element base 2b in the state that the driving pin 5 is not completely depressed. When the turntable 2 tends to rotate in this state, the hub 6 is rotated together with the rotation of the turntable 2 since the magnetically attracting force of the contacting portion is strong. (Since the hub 6 is attracted through the slider plate 4 in a normal state (FIG. 7), it does not rotate together with the turntable 2, but slides on the slider plate 4.) In other words, the chucking operation is mistaken to rotate the hub 6 irrespective of the rotatably driving force of the driving pin 5. When this chucking mistake occurs, the initial position of recording and reproducing on the disk 7 is in error to reduce the recording and reproducing accuracy.